WASHINGTON — The Space Launch System (SLS) heavy-lift rocket will use a modified Delta 4 upper stage provided by Boeing Co. for its first two missions, according to the terms of an eight-year, $175 million contract NASA announced July 23.
Boeing’s contract includes options for NASA to order two additional upper stages for SLS flights beyond 2021. If NASA exercises these options, Boeing’s contract will be worth $307 million over 12 years. Boeing will also provide flight spares for any rocket stages ordered by NASA. SLS will launch the Lockheed-built Orion Multi-Purpose Crew Vehicle to the Moon and back in 2017 and 2021. Only the second mission will be crewed.
The so-called Interim Cryogenic Propulsion Stage that NASA’s Marshall Space Flight Center in Huntsville, Ala., is buying from Boeing is powered by the same Pratt & Whitney Rocketdyne RL-10 engine that powers the Delta Cryogenic Second Stage (DCSS) on which it is based.
NASA says that Delta 4’s 5-meter upper stage requires relatively minor modifications to be used for SLS missions. The modifications include adding redundancy and increasing design margins to make the DCSS suitable for manned missions and either stretching the liquid hydrogen stage a matter of centimeters or using the DCSS attitude control system for a final, third burn for additional performance.
NASA announced Boeing’s award in an online post explaining the agency’s reasons for sole-sourcing the contract. NASA said it received three proposals for an interim cryogenic propulsion stage, but that only Boeing’s could meet the agency’s requirements “with relatively minor modifications.” Boeing will have to complete these modifications and deliver the first of the two stages to NASA by Sept. 30, 2016.
Before ordering Delta 4 upper stages from Boeing for any flights after 2021, NASA must conduct a formal review of alternative engines, the agency said in its July 23 “Justification for Other Than Full and Open Competition.”
By law, SLS must eventually be capable of lifting 130 metric tons to orbit. The version of the rocket that flies in 2017 and 2021 will be capable of lifting only about 70 metric tons using two five-segment, side-mounted solid-rocket motors provided by Alliant Techsystems, four space shuttle main engines provided by Pratt & Whitney Rocketdyne, and the modified Delta upper stage provided by Boeing.
To lift 130 metric tons, SLS will need new and more powerful side-mounted boosters and a different upper stage. On July 13, NASA announced it will spread $200 million of study money among four companies to study options for advanced boosters. The competition to build the boosters will not start until 2015.
Meanwhile, Pratt & Whitney Rocketdyne is already working on the J-2X upper-stage engine that more powerful SLS variants will use to lift heavy cargo such as the landing craft and habitation modules that NASA says it needs for future human exploration missions beyond Earth orbit. NASA has yet to announce an SLS mission that will use a J-2X.